A biological optical measurement instrument is a device that is capable of irradiating a living body with near infrared rays and detecting light passed through the inside of the living body or reflected by the inside of the living body to simply measure blood circulation, hemodynamics and a variation of Hb inside the living body with less restraint and non-invasiveness to an object. In recent years, a technique that images measured data obtained from a plurality of measurement regions of a living body using a multi-channel device has been realized, and is expected to be applied to clinical tests.
In the biological optical measurement instrument, a semiconductor laser (hereinafter, abbreviated as LD) for emission of near infrared rays is used. It is known that the LD has temperature dependency on electric characteristics (threshold current, driving voltage and the like) or optical characteristics (optical output, wavelength and the like).
In the biological optical measurement instrument, a living body is irradiated with near infrared rays of a predetermined output, and a variation of Hb is calculated by light passed through the inside of the living body or reflected by the inside of the living body and an absorption coefficient value of Hb in blood. The absorption coefficient value of Hb in blood varies according to a wavelength value of the near infrared rays. Thus, if electric characteristics and optical characteristics vary according to a temperature change in an LD, the wavelength value of the near infrared rays varies, and thus, the absorption coefficient value of Hb also varies, which affects detection of the variation of Hb.
In this regard, PTL 1 discloses a technique that controls a driving voltage according to a driving current of an LD to stabilize a wavelength of the LD. PTL 2 discloses a technique that corrects a temperature of an LD using a Peltier element to reduce a wavelength variation.
PTL 3 discloses a technique that corrects a parameter such as an absorption coefficient value of Hb according to a temperature change in an LD in a calculation process of the concentration of oxy Hb or deoxy Hb in an optical measuring device such as an oxygen monitor to correct a wavelength variation due to the temperature change in the LD.